Field of the Disclosure
The present invention relates generally to switched mode power converters utilizing a Bipolar Junction Transistor (BJT) as a switching element. More specifically, the present invention is directed to the measurement and prediction of the BJT storage time to provide a sufficient turn-off delay time for the improved performance of a power converter.
Background
Electronic devices (such as cell phones, tablets, laptops, etc.) use power to operate. Switched mode power converters are commonly used due to their high efficiency, small size, and low weight to power many of today's electronics. Conventional wall sockets provide a high voltage alternating current. In a switching power converter, a high voltage alternating current (AC), 50 or 60 Hz, input is converted through high frequency (HF) switching of a switching element with controlled on and off states to provide a well-regulated direct current (DC) output through an energy transfer element to a load. The desired output is provided by varying the duty cycle (ratio of the on-time to the total switching period, known as pulse width modulation (PWM), varying the switching frequency, which is known as pulse frequency modulation (PFM), or by skipping some switching pulses per the load change requirement, which is known as on-off control.
With stringent energy saving regulations for power converters, there are continuing efforts to provide improved operation and high efficiency in power converters. One important parameter in an improved and efficient power converter is an optimized switching function. Switching elements of the power converter affect the efficiency of the power converter by contributing to both the conduction loss and switching loss, which form a major part of the power loss in the power converter.
MOSFET, BJT, IGBT or other types of semiconductor switches may be used in switched mode power converters as a switching element. Each of these types of electronic/semiconductor switches may require specific driving provisions for efficient performance. BJT switches are fast and efficient devices for switching. However, due to their junction stored charge, BJT switches require special provisions in order to have an efficient turn off.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.